1. Field of the Invention
This invention relates to a process for producing a vinylidene fluoride copolymer, particularly to a process for producing a vinylidene fluoride copolymer having excellent flexibility, impact resistance and cold resistance.
2. Description of Prior Art
Polyvinylidene fluoride has excellent weathering resistance, corrosion resistance, electrical characteristics, processability, etc., and therefore has been used in a diversity of uses.
However, since polyvinylidene fluoride has great crystallinity, residual stress during processing is great, susceptible to formation of stress cracks with lapse of time, also lacks flexibility, with impact resistance and cold resistance being also inferior as compared with other fluorine resins. Accordingly, for improving flexibility, impact resistance and cold resistance, there have been proposed, for example, the method in which vinylidene fluoride is copolymerized with another monomer, such as hexafluoropropylene, tetrafluoroethylne, methyl methacrylate, butyl acrylate, etc., or the method in which an acrylic resin, etc. is formulated in polyvinylidene fluoride.
However, the copolymer obtained by the method of the prior art of copolymerizing vinylidene fluoride with another monomer has excellent flexibility, but has such problems that the melting point is lowered to lower the usable temperature region, or that processability is lowered. On the other hand, the composition obtained by the method of formulating an acrylic resin, etc. in polyvinylidene fluoride has excellent transparency, processability and flexibility, but has such problems that weathering resistance and chemical resistance are worsened.